1. Field of the Invention
The invention relates to a truck which has front wheels provided under the front part of a forked bed and a rear wheel provided under a hydraulic pressure cylinder for raising or lowering the bed.
2. Background Art
As disclosed in Japanese Utility Model Application Publication No. 58-23740, a truck that can be moved backward and forward in the longitudinal direction by a pair of wheels or right and left in the lateral direction by another pair of wheels, both of the pairs of which are rotatably fixed under a the front part of the bed of the truck with arms put in between, and is provided with a rear wheel which is fixed under a hydraulic pressure cylinder and capable of turning to the right and the left with a pumping handle which also works the hydraulic pressure cylinder has been known prior to the present invention.
In the prior art, the paired wheels of the truck which roll in the lateral direction are raised up from the ground by the force of a spring connecting the bed and the arms when the other paired wheels come in touch with the ground. However, the spring is put in so narrow a space between the side of the bed and the arms that its size and length have to be limited. Briefly, a stronger spring with greater diameter and greater number of turns is in fact needed but cannot be used in such a conventional truck due to the narrow space. Since the spring has to be smaller and weaker than it should be, it cannot bear long hard works and sometimes is liable to break down by oxidation corrosion. Therefore, more than one spring is actually needed to raise the wheels and, accordingly, there are problems in safety as well as in its structure.